Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

Show paginator

Hide paginator

25%

Page 1 of 4

1. For obtaining high COP, the pressure range of compressor should be

Any value

High

Optimum

Low

2. In a refrigeration system, heat absorbed in comparison to heat rejected is

Less

More for small capacity and less for high capacity

Same

3. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Normal cooling

Sub-cooling or under-cooling

Super-cooling

4. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Unpredictable

Less

Equally

5. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

3.33

4.33

1.33

6. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

7. Critical temperature is the temperature above which

A gas will immediately liquefy

Water will never evaporate

A gas will never liquefy

Water will evaporate

8. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Superheated vapour

Wet vapour

Dry saturated vapour

9. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

2.15

5.12

1.25

10. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Near critical temperature of refrigerant

Above critical temperature

Page 2 of 4

11. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(B) Heat stored in the human body

(D) Difference of (A) and (B)

(A) Heat dissipated to the surroundings

12. Most thermostatic expansion valves are set for a superheat of

10°C

5°C

20°C

15°C

13. Freon group of refrigerants are

Inflammable

Toxic

Non-inflammable and toxic

Nontoxic and non-inflammable

14. The capillary tube, as an expansion device, is used in

Room air conditioners

All of these

Water coolers

Domestic refrigerators

15. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant temperature

Takes place at constant pressure

Takes place at constant entropy

Involves no change in volume

16. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

17. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

18. In a lithium bromide absorption refrigeration system

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

19. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.376

0.6

0.4

0.67

20. The curved lines on a psychrometric chart indicates

Wet bulb temperature

Dry bulb temperature

Relative humidity

Dew point temperature

Page 3 of 4

21. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Receiver and evaporator

Compressor and condenser

Condenser and receiver

22. A thermostatic expansion valve in a refrigeration system

None of the above

Maintains different temperatures in evaporator in proportion to load

Ensures the evaporator completely filled with refrigerant of the load

Is suitable only for constant load systems

23. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Centrifugal

Piston type reciprocating

Axial

24. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Negative

Zero

Positive

None of these

25. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Freon

Carbon dioxide

Ammonia

26. The vapour compression refrigerator employs the following cycle

Rankine

Reversed Carnot

Reversed Rankine

Carnot

27. Rating of a domestic refrigerator is of the order of

0.1 ton

5 tons

10 tons

40 tons

28. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

9: 1

1: 9

1: 3

29. The bank of tubes at the back of domestic refrigerator is

Condenser tubes

Evaporator tubes

Refrigerant cooling tubes

Capillary tubes

30. Cooling water is required for following equipment in ammonia absorption plant

Condenser, absorber and separator (rectifier)

Condenser

Absorber

Evaporator

Page 4 of 4

31. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

Detect liquid in vapour

32. Which of the following is not a desirable property of a refrigerant?

Low boiling point

Good electrical conductor

Large latent heat

High risibility with oil

33. Which of the following cycles uses air as the refrigerant?

Stirling

Carnot

Ericson

Bell Coleman

34. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Always less than unity

Always more than unity

Equal to unity

35. Which of the following statement is correct?

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(D) Both (A) and (B)

36. The minimum temperature to which water can be cooled in a cooling tower is

Dew point temperature of air

Wet bulb temperature of air

Dry bulb temperature of air

Ambient air temperature

37. The operating pressure for refrigerating units using R-12 as a refrigerant is

15 bar

30 bar

2 bar

8 bar

38. The freezing point of sulphur dioxide is

-135.8°C

-75.2°C

-77.7°C

-56.6°C

39. A bootstrap air cooling system has

One heat exchanger

Four heat exchangers

Three heat exchangers

Two heat exchangers

40. The boiling point of ammonia is

-30°C

-10.5°C

-77.7°C

-33.3°C

Share this Now with Friends:

VideRime

A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

Related

Leave a ReplyCancel reply

Ads by Google

Recent Posts

Membership Registration

Secured Payment

Protection